Multiscale compatibility mechanisms and long-term oxidative aging resistance of chemically grafted waste tire rubber-modified asphalt

To improve the compatibility and laboratory-aged durability of waste-tire-derived crumb rubber (CR)-modified asphalt, maleic anhydride-grafted crumb rubber (CR-g-MAH) was prepared through benzoyl peroxide-initiated free-radical grafting. Molecular dynamics simulations, microscopic characterization, rheological testing, and chemical aging analysis were combined to investigate the interfacial mechanism and binder-level performance after rolling thin-film oven (RTFOT) and pressure aging vessel (PAV) conditioning. FTIR results were consistent with the presence of MAH-related functional groups after purification and suggested possible ester-related interactions, while simulations indicated that CR-g-MAH/asphalt exhibited the strongest relative modeled interactions and the lowest modeled chain mobility. CR-g-MAH asphalt displayed a more diffuse interfacial transition zone, more uniform rubber dispersion, and the lowest softening-point difference (2.1 °C). It also exhibited improved rutting resistance, stress stability, and low-temperature relaxation retention. After PAV conditioning, its fatigue life at 2.5% strain was 7.7 times that of base asphalt, although it remained lower than that of conventional CR asphalt. CR-g-MAH asphalt also exhibited the smallest FTIR-based carbonyl-index increment (0.017). This study provides a mechanistic basis for improving the compatibility and laboratory oxidative-aging resistance of CR-modified asphalt binders.